CVE-2026-25656: Siemens Sinec NMS RCE Vulnerability

CVE-2026-25656 Overview

A high-severity DLL hijacking vulnerability has been identified in Siemens SINEC NMS and User Management Component (UMC) that allows low-privileged attackers to escalate privileges to SYSTEM level. The vulnerability exists due to improper modification controls on a configuration file, enabling attackers to load malicious DLLs and achieve arbitrary code execution with the highest system privileges.

This vulnerability poses significant risk to industrial control system (ICS) environments where Siemens SINEC NMS is deployed for network management. Successful exploitation could grant attackers complete control over affected systems, potentially compromising critical infrastructure operations.

Critical Impact

Low-privileged local attackers can achieve arbitrary code execution with SYSTEM privileges through DLL hijacking, potentially compromising entire network management infrastructure.

Affected Products

• Siemens SINEC NMS (All versions)
• Siemens User Management Component (UMC) (All versions < V2.15.2.1)

Discovery Timeline

• 2026-02-10 - CVE-2026-25656 published to NVD
• 2026-02-12 - Last updated in NVD database

Technical Details for CVE-2026-25656

Vulnerability Analysis

CVE-2026-25656 is classified under CWE-427 (Uncontrolled Search Path Element), a vulnerability type that enables DLL hijacking attacks. The affected Siemens applications fail to properly restrict modification of configuration files that influence DLL loading behavior. When a low-privileged user gains the ability to modify these configuration settings, they can redirect the application to load malicious DLLs from attacker-controlled locations.

The vulnerability is particularly dangerous because the affected SINEC NMS application runs with elevated SYSTEM privileges. When the application loads a malicious DLL specified through the compromised configuration, the attacker's code executes in the context of the SYSTEM account, providing complete control over the affected host.

This vulnerability was reported through the Zero Day Initiative and tracked as ZDI-CAN-28108, indicating coordinated disclosure through a reputable vulnerability research program.

Root Cause

The root cause of this vulnerability is improper access control on a configuration file that determines DLL loading paths. The application fails to enforce appropriate restrictions on which users can modify this critical configuration file. By design, configuration files that influence code loading behavior should only be writable by administrators or the application itself. The permissive file permissions allow low-privileged users to inject arbitrary DLL paths into the application's configuration.

Attack Vector

The attack requires local access to a system running the vulnerable Siemens software. An attacker with low-privilege access performs the following steps:

1. Identify the vulnerable configuration file that controls DLL loading paths
2. Modify the configuration to point to a directory under attacker control
3. Place a malicious DLL with the expected filename in the attacker-controlled directory
4. Wait for or trigger the application to restart or reload configuration
5. The application loads the malicious DLL with SYSTEM privileges

The vulnerability mechanism exploits the Windows DLL search order when the application attempts to load required libraries. By manipulating the configuration file, attackers can insert a malicious DLL earlier in the search path than the legitimate library.

For detailed technical information, refer to the Siemens Security Advisory SSA-311973.

Detection Methods for CVE-2026-25656

Indicators of Compromise

• Unauthorized modifications to SINEC NMS or UMC configuration files, particularly those related to DLL paths or library loading
• Unexpected DLL files appearing in non-standard directories accessible by low-privileged users
• Suspicious process execution chains where SINEC NMS or UMC processes spawn unexpected child processes
• Windows Event Log entries indicating DLL loads from unusual paths by the affected applications

Detection Strategies

• Monitor file integrity of SINEC NMS and UMC configuration files using file integrity monitoring (FIM) solutions
• Implement Windows Sysmon logging to capture DLL load events (Event ID 7) for SINEC NMS processes
• Configure endpoint detection rules to alert on configuration file modifications by non-administrator users
• Deploy SentinelOne Singularity to detect and prevent unauthorized DLL loading and privilege escalation attempts

Monitoring Recommendations

• Enable audit logging for file system access on SINEC NMS installation directories and configuration paths
• Monitor for privilege escalation patterns where low-privilege user actions precede SYSTEM-level process execution
• Implement application allowlisting to prevent unauthorized DLL execution in the SINEC NMS directory structure
• Configure SentinelOne behavioral AI to detect DLL hijacking attack patterns in real-time

How to Mitigate CVE-2026-25656

Immediate Actions Required

• Update Siemens User Management Component (UMC) to version V2.15.2.1 or later immediately
• Review and restrict file permissions on SINEC NMS and UMC configuration files to administrators only
• Audit systems for signs of prior exploitation, including unexpected DLL files and configuration changes
• Implement network segmentation to limit lateral movement potential from compromised systems

Patch Information

Siemens has released security updates to address this vulnerability. Organizations should apply the following patches:

• User Management Component (UMC): Update to version V2.15.2.1 or later
• SINEC NMS: Monitor the Siemens Security Advisory SSA-311973 for patch availability

Review the official Siemens security advisory for complete patch information and installation guidance. Given the industrial control system context, ensure patches are tested in a staging environment before production deployment.

Workarounds

• Restrict configuration file permissions using Windows file ACLs to allow modification only by SYSTEM and local administrators
• Implement application allowlisting using Windows AppLocker or similar solutions to prevent unauthorized DLL execution
• Deploy SentinelOne Singularity endpoint protection to detect and block DLL hijacking attempts in real-time
• Consider operating the affected systems in restricted network segments with limited user access until patching is complete

# Windows command to restrict configuration file permissions (adjust path as needed)
icacls "C:\Program Files\Siemens\SINEC NMS\config" /inheritance:r /grant:r "SYSTEM:(OI)(CI)F" /grant:r "Administrators:(OI)(CI)F"